fix(ui): remove empty substrate template metadata

[mikemikimike]

Summary / Problem

Fixes #2653. After Actor Templates moved from Kubernetes CRDs to ate-api in #2638, goldenActorId, harnessName, and managedByKagent are no longer available from the served ate-api template. The Substrate page consequently exposed values that were always empty or dead.

Changes

• Remove the unavailable metadata from the internal Go inventory model and gRPC serialization path.
• Remove the corresponding TypeScript domain fields, client mapping, mock data, and the Substrate table's golden-actor and Harness projections.
• Keep the existing v1alpha1 wire fields for backward compatibility; the server no longer populates them and the UI no longer depends on them.
• Add a browser regression assertion that the removed columns and golden-actor display do not reappear.

Tests

• go test -skip 'TestE2E.*' ./core/internal/service/system ./core/internal/grpcserver — passed.
• go vet ./core/internal/service/system ./core/internal/grpcserver — passed.
• golangci-lint v2.13.0 with the repository's enabled checks except the Windows-incompatible kube-api-linter plugin — 0 issues.
• go run github.com/bufbuild/buf/cmd/buf@v1.72.0 lint — passed.
• go run github.com/bufbuild/buf/cmd/buf@v1.72.0 generate — passed with no generated drift.
• go run github.com/bufbuild/buf/cmd/buf@v1.72.0 breaking proto --against ".git#branch=main,subdir=proto" — passed.
• corepack yarn typecheck — passed.
• corepack yarn lint — passed with 0 errors and 7 pre-existing warnings.
• corepack yarn test — 34 files and 412 tests passed.
• corepack yarn build — passed.
• corepack yarn playwright test playwright/tests/substrate --project=chromium --project=firefox — 16 tests passed.
• git diff --check — passed.

Compatibility / Known limitations

The Substrate Actor Templates table no longer displays the three fields that ate-api cannot provide. The protobuf fields remain on the wire so existing clients are not broken, but they are no longer populated by this service. Full Go CI race tests were not completed locally because Windows has CGO_ENABLED=0 and no cgo compiler; the repository's kube-api-linter plugin is also Unix-only. The full browser suite was attempted: 173/179 passed, with 6 unrelated Firefox concurrency/mock-stream failures; the focused Substrate suite passed in both engines.

Issue

Issue: #2653 — #2653